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Introducing the Tink cryptographic software library

Thursday, August 30, 2018

Cross-posted on the Google Security Blog
At Google, many product teams use cryptographic techniques to protect user data. In cryptography, subtle mistakes can have serious consequences, and understanding how to implement cryptography correctly requires digesting decades' worth of academic literature. Needless to say, many developers don’t have time for that.

To help our developers ship secure cryptographic code we’ve developed Tink—a multi-language, cross-platform cryptographic library. We believe in open source and want Tink to become a community project—thus Tink has been available on GitHub since the early days of the project, and it has already attracted several external contributors. At Google, Tink is already being used to secure data of many products such as AdMob, Google Pay, Google Assistant, Firebase, the Android Search App, etc. After nearly two years of development, today we’re excited to announce Tink 1.2.0, the first version that supports cloud, Android, iOS, and more!

Tink aims to provide cryptographic APIs that are secure, easy to use correctly, and hard(er) to misuse. Tink is built on top of existing libraries such as BoringSSL and Java Cryptography Architecture, but includes countermeasures to many weaknesses in these libraries, which were discovered by Project Wycheproof, another project from our team.

With Tink, many common cryptographic operations such as data encryption, digital signatures, etc. can be done with only a few lines of code. Here is an example of encrypting and decrypting with our AEAD interface in Java:

Tink aims to eliminate as many potential misuses as possible. For example, if the underlying encryption mode requires nonces and nonce reuse makes it insecure, then Tink does not allow the user to pass nonces. Interfaces have security guarantees that must be satisfied by each primitive implementing the interface. This may exclude some encryption modes. Rather than adding them to existing interfaces and weakening the guarantees of the interface, it is possible to add new interfaces and describe the security guarantees appropriately.

We’re cryptographers and security engineers working to improve Google’s product security, so we built Tink to make our job easier. Tink shows the claimed security properties (e.g., safe against chosen-ciphertext attacks) right in the interfaces, allowing security auditors and automated tools to quickly discover usages where the security guarantees don’t match the security requirements. Tink also isolates APIs for potentially dangerous operations (e.g., loading cleartext keys from disk), which allows discovering, restricting, monitoring and logging their usage.

Tink provides support for key management, including key rotation and phasing out deprecated ciphers. For example, if a cryptographic primitive is found to be broken, you can switch to a different primitive by rotating keys, without changing or recompiling code.

Tink is also extensible by design: it is easy to add a custom cryptographic scheme or an in-house key management system so that it works seamlessly with other parts of Tink. No part of Tink is hard to replace or remove. All components are composable, and can be selected and assembled in various combinations. For example, if you need only digital signatures, you can exclude symmetric key encryption components to minimize code size in your application.

To get started, please check out our HOW-TO for Java, C++ and Obj-C. If you'd like to talk to the developers or get notified about project updates, you may want to subscribe to our mailing list. To join, simply send an empty email to tink-users+subscribe@googlegroups.com. You can also post your questions to StackOverflow, just remember to tag them with tink.

We’re excited to share this with the community, and welcome your feedback!